thevirginian

I have been reading and hearing about the pros and cons of power expanders for large scale airplanes. Many say it is a must for 30-40%, but just as many pilots are opposed to this opinion. I don't want o open a can of worms here, but I would like to hear what's really behind this " gadget". I have been flying large scale airplanes for a few years without the use of any electronic devices other than the straight servos, receiver and dual battery packs. Even with four digital servos for ailerons going into one channel in the receiver I never had a problem so far. I always programmed the linked servos thus eliminating any fighting among them. I am planning to run these new A123s in a redundant configuration in my new WH Sukhoi 26. Now do I need an expander or not before I spend another $150 for a nice "useless" piece of electronic that could go wrong?

Taildragger726

I am not comfortable with more than one high powered servo per lead. If you have enough ports on your reciever,and the mixing ability, go for it! [sm=thumbs_up.gif]

cygnet

My Feedback: (33)

If you haven't used a power expander yet and your systems work why even think about changing, I'm like you I fly 35 and 40% stuff and never use a power expander just keep it simple and you will be fine. Just my .02

camss69

My Feedback: (46)

It's just another device added to the system that can fail.

yarom

My Feedback: (82)

I have been using the Power Expander on anything above 30% for a while.

The main reasons were the need to provide proper current to the servos (5955s and up) and isolate a bad battery, if one was to fail.

The advent of the new HD receivers from JR/Spektrum and A123 batteries, made the power expander redundant and allows you to feed safely two batteries straight into the receiver and use the receiver safe switch, thus removing a lot of stuff from the airplane: regulators, switches and other gizmos.

If you use use Hitec servos, you can program them properly and even remove equalizers and other mixing gadgets, once necessary for ganging multiple servos on a single surface.

The whole thing makes for a very simple installation with minimal failure points.

I would not do this with any other type of receiver...

thevirginian

yarom, I used a 7 channel Spectrum in my previous giant scale (100cc) with four Hitec digitals ganged into one channel-no problems. I powered all that with a redundant 2400x2 Nimh packs and nothing else. Of course, the servos were properly programmed. So, if I use thee new A123s I would not need a Power Expander? My new servos are six HiTec 5985s and one 7988TG for the rudder.

Taildragger726

How did you do that?

Hammbone

My Feedback: (309)

A standard connector is rated at 3 amps.
This is just not sufficient for large scale planes, or planes with high current flow.
I set-up my planes so that I never have more than one servo downstream of any standard connector.
In order to do this, I have 2 options. I can use a Power Expander, or I can use a JR Powersafe rx.
I do not use "Y"s. Every servo gets its own power supply lead.

The worst thing you can do is use a standard connector between your battery and your rx. How many servos are downstream of a standard connector now?


Will a giant scale plane fly with the "old fashioned" simpler type set-up? Sure, but you will have limited current flow. Your servos will still work, but they will be weak. Less current flow = less torque and less speed.

Do you want to fly with limited current flow? or do you want to supply your servos with proper current flow?
It's your plane, the choice is yours.


Jim

thevirginian

Hammbone;
I realize the way I did it in the past was anything than perfect. Now I want to do it the right way, and that's why I seek you guy's advice

Hammbone

My Feedback: (309)

That's what these forums are good for.

My post wasn't meant just for you, but as friendly advice for everyone, take it or leave it.

Jim

mrbigg

My Feedback: (21)

Want a cheap, foolproof way to power up your plane? Save your cash and do some soldering. This is what I do and it has been flawless. I'll tell you how I set my 85" Ultimate up.

It has 2 Fromeco 4 cell packs for the reciever, running through their flag pin switch/regulator. Use your favorite switch and battery combo.
I have three 8611's in the tail. I took the output from the regultator (use the output from the switch if not usint a regulator) and soldered a Female Deans plug on. With the tail servos plugged into the reciever, I picked a spot where I could splice into the positves and negative wires. Leave the signal wire alone. Next I stripped all 12 ends, 6 positve and 6 negative. Then I twisted the positives together and then the negatives. Then they were soldered together. Next they were soldered to a Male Deans plug. Now when the Female Deans plug is plugged into the Male Deans plug, you have power going straight to the servos and into the reciever also. Simple and effective.
I also have four 8611's on the ailerons. The second battery is tapped into these servo's wires the same way. The throttle and choke servo get their power from the reciever.
This is a little time consuming, but not hard. Cheap and nothing that can fail.

Tired Old Man

My Feedback: (1)

I've had both the large and small W/H Sukhois. There was no need for a power expander on either one of them. As far as planes using ganged servo installations, I have a 35% Edge, a Comp Arf 2.6m Yak, a 41% Giles 202, and a 35% Giles 202. Everything uses standard connectors between the regulator and the receiver. The connections between batteries and the switch/regulators are 20 Amp Anderson Power Poles.

The number of amps pulled is largely dependant on the cleanliness of the set up. Clean, well balanced, matched servo installations with little or no binding that don't hit the servo stops don't draw that many amps. Poorly set up servo installations pull the big amp numbers. Always have, always will.

thevirginian

I am sorry, Taildragger
I misunderstood. Of course I don't have four aileron servos "ganged" into one channel. What I meant was I have two and two aileron serevos y-harnessed together and then y-harnessed all into one channel. My bad, I didn't pay closer attention.

Hammbone

My Feedback: (309)

I'm trying to follow your logic in using 20amp connectors into the regs, but standard 3amp connectors out of the regs? One weak point in the system limits the current flow everywhere.
Can you explain this?

Jim

thevirginian

Hey, tired old man (alias silversurfer )
So what your are saying is if I thoroughly program my servos and make sure they don't bind one another with my aileron hook up I should be O.K.? See, that's exactly the contraversy I am facing. Some people believe in this stuff some don't. I don't understand enough in electronics to know who is wrong and who is right.

Hammbone

My Feedback: (309)

Servo binding will use excess current. It also depends on how you fly, how much you demand from your servos. If you just fly around in lazy circles, that's not much of a load on the servos.
I've seen reports from people saying they have recorded (with in flight data equipment), using as much as 22amps in bursts on a 35% plane, and as much as 42amps in bursts on a 40% plane. If you want to use a connector rated at 3amps, the choice is yours.

Jim

Tired Old Man

My Feedback: (1)

I use things like Matchboxes and multi lead regulators. Three wire regulators to be accurate. When I plug two of the regulator power leads into a receiver it's the same as connecting 6-8 amps worth of supply to the receiver. I don't know where people came up with a 3 amp limitation on gold plated standard connectors but the melting point is a little over 4 amps. With the silicone insulated wires, ala Cermark, they melting point of the insulation is about the same.

So in using two power supplies, as you would with most of the power espanders, and two regulators, unlike a power expander, I can provide 4 power leads to the receiver. Now if I wanted to I could directly power a couple of Matchboxes with two regulators without going through the receiver at all. So now I can have 8 or more amps going to the receiver from two regulator plugs, or less if I desire. I can power up to a pair od Matchboxes from those same regulators if I desired. There's a tremendous number of options open for those that do a little research and understand how things work.


Now I just happen to use on board data systems as well and pulling the two worst maneuvers I can thing of, which is a wall and a blender at speed, I've never seen anywhere close to 20 plus amps. I don't fly anything smaller than 28% and prefer to fly 35%. In setting up a 3.1 m Comp Arf Extra for a guy using 4 ganged rudder servos the idle draw was about 6/10 of an amp with a load in the area of 2 amps. Then again, none of the linkage was binding, the servos were not driven to the stops, they were not fighting each other the surfaces did not bang against the linkage, and the wire runs and sizes were appropriate to the length of the run.

So it comes down to how much amperage do you really need? Are you trying to provide all the power that a stalled servo will draw? Hopefully not because you should be setting up the system so that a servo will NEVER stall. Matching servos, sizing servos to the applications, servo travels, linkage lengths and heights, holding a little short of max servo travel rotations, wire length and sizing, limiting connector quantities, and mechanical advantages is what makes everything work.

For those that are hung up on accessory advertising there will never be more ways than there are popular (for the moment) accessories. Understand that those selling the accessories much prefer that there's is the only methods recognized as safe and effective. That's what sells product and makes profits. That and sponsorships where a large number of people competing never paid for these products They were given to them in payment for promotion. Some of what I like to call "gimmick" examples are engines with magnetos versus engines with ignition systems. One will not provide more power than the other. A step further are ignitions with a mechanical advance and those with auto advance. Neither is better but one sells for more money that the other. Same with mag versus ignition engines. Ignition equipped engines sell for more. Do we need 300 oz in servos on our ailerons? Not at all but it makes good copy to advertise the big numbers because it makes for larger dollar volume.

No single widget is going to make a system work correctly. A good understanding of how the system works will go a lot father in that respect.

Hammbone

My Feedback: (309)

The 3 amp rating on standard connectors comes from the manufacturer.

You use matchboxes and regulators. These items can fail just as easy, or more often than a Power Expander does. I choose to use a Power Expander and I don't use regulators or matchboxes.

I can argue that my system is actually simpler than yours. All I have is 2 batteries into the Power Expander, with one failsafe switch, the Power Expander then powers my rx and all my servos.
You're right when you say there are many different ways to do the same thing, but I don't understand what many of you guys have against Power Expanders. There is really no simpler way to provide proper current flow than to use a Power Expander.

You don't have to use the top of the line, $600 PowerBox from Duralite. They have many different styles of Power Expanders to meet different needs with prices starting at about $100.

Jim

thevirginian

O.K.
Hammbone is for a reasonably priced Powerexpander like the Powerexpander Pro for $149.00 that has battery separation called "Smart sense". I like that idea alone very much. The other is that I can use A123's or 5 cell NiMh directly plugged in and any receiver like the Spectrum 7 channel. I know there are many ways to skin a cat but which one makes you feel most comfortable. One friend of mine flies his H9 Extra withtwo Matchboxes, anothe rflies his Extra with the PE Pro. Both love their choices and praise the products they are using. Both are excellent pilots and like security. Now who is right and who is wrong? I believe both are right in their own way. It boils down to personal preference and kowledge. So I guess I will decide whether I buy a coupl of Matchboxes or a PE Pro from Smart-Fly. Certainly I will not fly the way I used to fly, without any safety added.

Tired Old Man

My Feedback: (1)

Seems we have different manufacturers. I was told 4 amps and I know I have deliberately pushed up to 6 to see what happened. It got hot but it held.

The only thing I really have against a power expander is that they seem to limit servo voltages to 6v or less. Some people, myself included, have been using more than 6v for a long, long time and prefer it that way. I'm not going to state how many volts so nobody will be able to say what is or isn't safe, but with only 6v or less to start with you will never see 6v at a servo. If you have long servo extension you might be lucky to see 5v.

If I was doing an installation on a plane that only used one servo per surface I would only use one flight battery. Regulated or not would depend on the battery type. With any good computer radio you can use a mix to handle a pair of elevator servos so that negates the need for a Power Expander, Matchbox, MSA-10, or SmartFly Equalizer.

thevirginian

You got a point, silversurfer. I've been using 6V straight for many years without a single glitch and I am a strong believer that these 6V are no harm to the servos or receiver. One time I accidently plugged in a freshly charge LiPo pack without a regulator and it didn't fry anything.

Hammbone

My Feedback: (309)

Power Expanders do not limit voltage. What you put in is what you get out.

I'm not that familiar with the Duralite stuff, maybe they have built in reg's, I don't know.
I use the Smart fly Power Expanders, and what you put in is what you get out. It does provide filtered and regulated, 5v power to the rx, but servo current is not regulated. I'm using unregulated A123's, so I'm operating at 6.6v.

Jim

thevirginian

Hammbone,
That's the way I read the product info from Smart-Fly. Now, does it also compensate for long servo leads?

OldRookie

My Feedback: (13)

Is it possible to hook in a 16 or 18 gage wire, directly to the power buss of the receiver?
This would allow you to use heavy gage wire, and a Deans plug to power the receiver and servos.

Greg

Tired Old Man

My Feedback: (1)

From the Power Expander Pro instruction sheets:

"It is highly recommended that you beef up the power wiring between
the battery and the PowerExpander Pro above the standard 22ga wiring.
Failure to do this will diminish the effectiveness of the PowerExpander
Pro at providing the highest possible voltage to the servos. Servos
operating at lower voltages produce less torque than they are rated at."

Nothing against the use of a Power Expander, but this is the same thing you should do if not using a Power Expander. If you pay attention to your connections and power supplies what's the point of buying and using another accessory? It's between the servos and the power supply that more current capability is needed.

As far as amperage running through a receiver, when the tests were performed on JR receivers a few years back the testing was stopped after proving that their products could handle 60 amps. That not to say they were limited to 60 amps, but they did not test any further believing that no one would ever have a need to obtain 60 amps, let alone more.
We're victims of our own fear and much too gimmick conscious I'm afraid.